1. Field of the Invention
The present invention relates to a gamma voltage generation circuit. More particularly, the present invention relates to a gamma voltage generation circuit used in LTPS (low temperature polycrystalline silicon) panels.
2. Description of the Related Art
FIG. 1 shows a traditional gamma voltage generation circuit. The gamma voltage generation circuit provides groups of gamma voltages for different colors to DACs (digital-to-analog converters). The gamma voltage generation circuit has resistor strings 105, 115, 125 and 135 respectively for red, green, blue and white, and buffers 191˜198. Each resistor string receives reference voltages through the buffers and outputs to a corresponding DAC the gamma voltages derived by division of the reference voltages. For example, the resistor string 105 for red receives reference voltages through the buffers 191 and 195, and outputs the gamma voltages to the DACs 103 and 107 for red.
FIG. 2 shows another traditional gamma voltage generation circuit. The main difference between the circuits of FIG. 1 and FIG. 2 is that the latter is adapted to DACs shared by red, green, blue and white channels. Thus, switches are included to selectively transfer to the DACs the group of the gamma voltages provided by one of the resistor strings. For example, the switches 205 and 206 are closed to transfer to the DACs 240 and 250 the group of the gamma voltages provided by the resistor string 105 when red channels are selected.
Both of the gamma voltage generation circuits described above include one resistor string for each color. These resistor strings consume a large circuit area. Moreover, using one resistor string for each color necessitates a large number of I/O pads, which also consumes a large circuit area.